Chlorofluorocarbons (CFCs) are synthetic chemical compounds widely used in refrigeration and air conditioning; as aerosol propellants and solvents; in forming foams, including those used in fast-food packaging; and in rigid insulation. Scientists now see these synthetic chemicals as the main threat to Earth's protective ozone layer. Because CFCs are immune to destruction in the troposphere, and because they eventually float upwardly, their manufacture and release have lead to the accumulation of large amounts in the stratosphere. In the stratosphere, CFCs are broken down by sunlight into chlorine, which has a catalytic and destructive effect on ozone. The result has been a significant decline in the global ozone shield and an increase in the amount of harmful ultraviolet radiation reaching the surface of Earth. According to a United Nations' study, every 1 percent drop in ozone will lead to a 3 percent increase in non-melanoma skin cancers in light-skinned people, as well as dramatic increases in cataracts, lethal melanoma cancers, and damage to the human immune system. Higher levels of UV light may also worsen ground-level pollution and hurt plants, animals, and especially light sensitive aquatic organisms.
As a result, destruction of CFCs, and in some instances, reclamation of CFC refrigerants is a vital component of the national and global strategies for protection of the earth's ozone layer in a manner consistent with minimal economic disruptions associated with the phase-out of this class of chemicals. There are still sizable reserves of CFCs on hand which must be treated and converted to environmentally benign substances. Likewise, until existing refrigeration and air conditioning equipment is replaced or retrofitted with devices which are capable of operating with more environmentally friendly refrigerants, as CFC production is curtailed and eventually eliminated, industry and consumers must rely increasingly on the availability of reclaimed refrigerants.
However, successful reclamation is presently hampered due to the occurrence of inadvertent contamination of refrigerants by other refrigerants. In order to qualify for reuse, reclaimed refrigerants are required to meet the American Refrigeration Institute's "700" specifications which stipulate the permissible levels of contaminants. That is, strict limits are placed on moisture, particulates, acidity, oil content, non-condensible gases, and other refrigerants present. Existing refrigeration and air conditioning equipment appears capable of employing reclaimed refrigerants. Existing reclamation processes are capable of meeting all of the foregoing criteria with the exception of "other refrigerants", which are not permitted to exceed 0.5 percent maximum.
One example of a widely found refrigerant mixture is Freon.RTM. 12, a trademark of E. I. DuPont, which is dichlorodifluoromethane, contaminated with Freon 22, which is chlorodifluoromethane, hereinafter called R-12 and R-22, respectively. Although removal of the unwanted R-22 contaminant from such a mixture would appear to be readily accomplished by distillation due to differences in their boiling points (R-12 b.p. -29.8.degree. C. and R-22 b.p. -41.degree. C.), separation by distillation is not readily achieved due to the formation of an azeotrope consisting of 75 percent R-22, when the two refrigerants become mixed.
Other known technologies for the destruction of CFCs such as thermal oxidation, catalytic decomposition, supercritical water oxidation, plasma destruction methods, biological processes, UV photolysis, and so on, are either in experimental stages of development, economically unattractive or incapable of selectively destroying the unwanted contaminating refrigerant without also eliminating the desired refrigerant.
Quite significantly, the present inventors discovered that solutions of a base, such as aqueous solutions sodium hydroxide and solutions of bases in organic solvents can be efficiently employed in highly economic processes of purifying contaminated refrigerant mixtures, including the recovery of purified refrigerant to readily meet the "other refrigerant" specification. Accordingly, the methods are especially useful in reclamation processes where production of certain CFCs, such as R-12 is being phased-out of production, but market demand remains strong.
The hydrolysis of chlorodifluoromethane (R-22) in aqueous sodium hydroxide was disclosed by Takao Hayashi in a paper entitled "Preparation of Sodium Formate by Hydrolysis of Chlorodifluoromethane", Kogyo Kagaku Zasshi, Vol. 68, No. 10, 2002 (1965). The studies were conducted with R-22 having a minimum specification of 99.9% CHClF.sub.2, 0.4% CCl.sub.2 F.sub.2 and 0.3% air. However, the R-22 reactant actually used in these studies was analyzed by gas chromatography to verify the compositional make-up. According to the author, apparently no refrigerant was detected other then the R-22 reactant. That is to say, while the R-22 refrigerant cylinder specification had allowed for a trace amount (0.4%) R-12, chromatographic analysis showed that none was found in the refrigerant reactant used in the studies.
Hayashi concluded that since it was apparently known that "dichlorodifluoromethane is not easily susceptible to being hydrolyzed, it seems that protonic hydrogen atom may make easy the hydrolysis of chlorodifluoromethane." The only objective of the Hayashi paper was to demonstrate the successful production of sodium formate by alkaline hydrolysis of chlorodifluoromethane (R-22), which was free of other refrigerant reactants. In addition, the earlier efforts of Hayashi did not include separation and recovery steps in order to retrieve a purified refrigerant, like R-12.
R. C. Downing in Fluorocarbon Refrigerant Handbook, Prentice Hall, 1988 (307-308) describes a series of studies in which R-22 alone and with R-12 was bubbled through solutions of sodium methylate in methanol. Downing disclosed the lack of stability and breakdown of R-22 which could be detected by the formation of a sodium chloride precipitate. The author reported R-12 was not similarly effected. In testing mixtures of R-12 and R-22 alcoholic sodium methylate the presence of R-22 at concentrations down to 5 wt percent was detected. In conducting his stability/analytical studies Downing failed to teach or suggest steps for recovering the more stable R-12 from refrigerant mixtures after treating with the base as a viable means in recycling refrigerants.
Accordingly, the methods disclosed herein effectively overcome the dilemma of reclamation of refrigerants containing more than 0.5 percent "other refrigerant." Methods heretofore failed either to recognize the ability of recovering useful refrigerants from contaminated mixtures, or were ineffective in selectively removing the contaminating refrigerant. With insufficient quantities of newly produced perhalogenated refrigerants like R-12 available to dilute hydrochloro-fluorocarbon refrigerants to acceptable levels, and environmental regulations prohibiting venting to the atmosphere the only readily available alternative has been costly incineration. This, however, does not allow for reclamation.